Process for removing acid components from hydrocarbon distillates



Patented Dec. 19, 1939 PROCESS FOR REMOVING ACID COMPO NENTS FROM HYDROOARBON DISTIL- LATES David Louis Yabrofi, Berkeley, Calif., assignor to Shell Development Company, San Francisco,

Calif., a corporation of Delaware No Drawing. Application February 7, 1939,

' Serial No. 255,100

6Clalms.

This invention is a continuation-in-part of my co-pending application Serial No. 102,893, filed September 28, 1936, which has issued as U. S.

Patent 2,152,166, March 28, 1939, and deals with; 5 the removal of weakly acid reacting organic substances from solutions in certain water-insoluble organic liquids by extraction with aqueous solutions of caustic alkali containing a solubility promoter for these substances, and more particularl ly deals with the removal of mercaptans from hydrocarbon distillates.

It is frequently necessary to eliminate small quantities of organic relatively weak acid reacting components such as mercaptans, phenols.

l thiophenols, alkyl phenols, fatty'acids, etc., from their solutions in neutral or weakly basic re acting organic liquids which are substantially immiscible with water such as the liquid hydrocarbons derived from petroleum, benzene, tol- 2o uene, xylene, substituted normally liquid hydrocarbons which are substantially insoluble in water, for instance, chlorinated hydrocarbons, of which chlorethane, ethylene dichloride, trichlorethylene, carbon. tetrachloride, chlorpropane,

. chlorbutylene, chlorbenzene, brombenzene, are examples; or nitrogen containing hydrocarbons such as amyl or higher amines, aniline, waterinsoluble pyridine derivatives, petroleum bases, etc.

30 In order that the water-insoluble organic liquids may be treated by my process, they must be substantially inert and resistant to chemical reaction with strong aqueous solutions of caustic alkali when contacted therewith for short periods 35 of time, e. g., about minutes or less at normal room temperatures.

My invention comprises extracting organic acids which are difilcult to extract, such as the weak acids having dissociation constants lower 40 than those of' fatty acids, e. g., mercaptans,

phenols, etc., contained in water-insoluble organic liquids which are substantially inert toward strong aqueous caustic alkali solutions at normal room temperatures, with an aqueous so- 45 lution of caustic alkali in which is dissolved a substantial amount'of a solubility promoter for weak organic acids, under conditions to absorb at least a major portion of the weak organic acids in the aqueous solution, and to form two 50 layers and separating the layers. v

In the application.Serial No. 102,893, filed September 28, 1936, I have disclosed that certain polar substances which are at least partly miscible with aqueous solutions of strong caustic 55 alkali, promote the solvent power for weak or-.

ganic acids of aqueous caustic alkali solutions in'which theyare dissolved. I have shown that among other compounds, certain glycols including propylene glycol are highly effective in the. matter of promoting the solubility of weak or- 5 ganic acids such as mercaptans, phenols, etc., in aqueous caustic alkali solutions. j

Aqueous solutions of various caustic alkalis may be used. The alkali metal hydroxides are most useful and efiective, although ammonia, M)

alkaline earth hydroxides, quaternary ammonium bases, alkali metal carbonates, etc., may also be suitable. V

The concentration of the aqueous caustic alkali may vary within wide limits. In general, I prefer to use caustic alkali solutions whichare above about 2 normal and preferably between 4 to 10 normal, calculated, on the total solution, although higher and lower concentrations may be used.

Concentration of the propylene glycol in the aqueous solution should preferably be between about and 75%, Moreover, the amount of water in the solution should be not less than 15% and not more than 70%, preferably not -more than 50%. The presence of water in the above 25 amount is highly desirable because otherwise the regeneration by steam stripping of spent alkaline v solutioncontaining solubility promoter and ab- I sorbed'weak organic acids is'extremely difilcult.

Thus steam consumption is greatly reduced .byf

the presence of-the preferred amounts of water, while on the other hand, the extraction efliciency for the weak acids need not be reduced materially. The presence of amounts of water greater than 15%- does not cause a substantial hydrolysis of dissolved alkali salts'of the weak organic acids as has been supposed by earlier investigators, the hydrolysis being largely a function of the alkalinity of the aqueous solution.

While increasing the amount of water may 40 have the additional advantage of reducing losses of the propylene glycol due to its being dissolved in the organic liquid, this is a minor consideration when treating hydrocarbon liquids, because propylene glycol is substantially insoluble in hydrocarbon liquids even in the presence ofamounts of water much smaller than 15%. 'I'hus,v for example, when contacting isooctane with 20 volume percent of aqueous solutions of propylene glycol containing 10 and 15% water, respectively, and analyzing the resulting isooctane for the glycol, it was found that in both cases the amount of glycol in the isooctane was somewhat below .01%, too small for accurate quantitati e determination. 66

7 eflicient K were found,

concentration of mercaptans in aqueous phase concentration of mercaptans in oil phase Solubility promoter 2.5N NaOH 5N NaOH None ethylene ethylene l. propylene glycol propylene glycol c lava Dl'O ZlXluZlC- glyeol o. a mera- The temperature of the extraction is preferably kept between 0 and C., the extraction efi'iciency decreasing with increases in the temperature; and at temperatures below about 0 C. difficulties are frequently encountered due to precipitation of a portion of the solubility promoter and/or excessive viscosity of the aqueous caustic alkali containing the solubility promoter.

The extraction of the organic acids from their solutions in the organic liquids described before be carried out by simply mixing the solution with a predetermined amount of the aqueous caustic alkali solution in which is dissolved a substantial amount of the propylene glycol, and then separating the liquids. The resulting aqueous solution contains most of the propylene glycol and the major portion of the organic acids, while the organic liquid stripped from the acids contains a trace of the glycol. By washing the stripped organic liquid with water, the propylene glycol is re-extracted by the latter. The aqueous solution so obtained may then be added to the caustic alkali solution containing the bulk of the glycol, and excess water may be separated from the resulting solution by distillation.

More thorough extraction may be had, however, in a multi-stage countercurrent extraction system or in a packed tower.

The amount of aqueous caustic alkali solution required in the extraction is normally above about 5% by volume and for economical reasons seldom exceeds about 100% by volume. Normally from about 10 to 50% by volume is used depending upon the required thoroughness of removing the weak organic acids.

Spent aqueous caustic alkali solution containing the propylene glycol and weak organic acids may be regenerated by distillation, steaming and/or oxidation, according to well-known principles.

The following examples further serve to illustrate my process:

A West Texas straight run full range gasoline containing .0699% mercaptan sulfur was extracted at 20 C. with 10 volume percent of 9. SN aqueuos caustic soda solution. 7.0% of the mercaptan sulfur was removed. The same gasoline was then treated under identical conditions with a 5N aqueous caustic soda solution containing 50% propylene glycol. 46.0% of the mercaptan sulfur was removed.

When treating a California light gasoline -boiling from 35 to 105 C. and containing .0137% mercaptan sulfur as above, the percentages of mercaptan sulfur removed were 41.5%' and 87.1%, respectively.

I claim as my invention:

1. In the process of separating organic acid reacting substances contained in a water-insoluble neutral or basic organic liquid, the steps comprising treating said liquid with an aqueous solution of a strong base containing a substantial amount of dissolved propylene glycol, said solution containing from 15 to water, under conditions to absorb at least a portion of said acid reacting substances in said aqueous solution and to form two liquid layers, one comprising the aqueous solution containing absorbed acid reacting substances, and the other consisting essentially of the treated organic liquid, and separating the layers.

2. The process of claim 1 in which the aqueous base solution contains between 25 and of the propylene glycol.

3. The process of claiml in which the aqueous base is from 2 to 10 normal.

4. The process of claim 1 in which the organic liquid is extracted with 5 to volume percent of aqueous base solution containing the propylene glycol.

5. The process of claim 1 in which the base is an alkali metal hydroxide.

6. In the process of separating mercaptans from hydrocarbon distillates containing same by extraction with an aqueous solution of a strong base, the improvement comprising extracting said distillate with at least 5 volume percent of a 2 to 10 normal aqueous alkali metal hydroxide solution in which is dissolved between 25 and 75% of propylene glycol, said solution containing from 15 to 70% water, under conditions to absorb at least a major portion of the mercaptans in the aqueous solution and to form two liquid layers, one comprising the aqueous alkali metal hydroxide solution containing substantially all of the propylene glycol and the major portion of the mercaptans, and the other consisting essentially of treated hydrocarbon distillate, and separating the layers.

DAVID LOUIS YABROF'F. 

